At this point I'd love for ANYONE to do another tournament level Marvel fighting game.
For the record Injustice isn't bad. Its just not super deep at its core list of tools and options. Its had all but 2 characters reach top 8, It sold enough to make a ton of profit, it has one of the most successful comics on the market (won some awards even), has one of the better phone game tie ins, and it was approachable at all levels of play to the public.
These aren't things that we should really knock on its lists of achievements. Its not the super deep and loud excitement of the Capcom Marvel fighting games, but its a fun game nonetheless.
An NRS Marvel at the very least would offer an interesting new reinterpretation of movesets to characters who have stayed similar for quite some time. I'd just want them to add things like dodge rolls, or projectiles canceling each other out to give it a faster pace and a nicer close game than Injustice had. Though if they gave us something more akin to the pace and stylings of the new MKX I can't say I'd be sad. That game looks really hype.
Honestly this would be the best answer in terms of profit. Think about it...Smash bros is approachable and addictive at all levels. You could have a ton of items and assist trophies from the Marvel Universe, Stage hazards could be from Marvel locations and story events, minigames would be fairly easy to come up with, collectibles would be easy to get folks addicted to considering you could make stickers cover art from comics, and bios, and overall it'd be a pretty enjoyable experience overall.
Make Marvel a Ringout Smash Bros clone? Hell yeah I'd sign on for that.